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Smoke

Smokeis a
collection of airbornesolidandliquidparticulatesandgasesemitted when a material undergoescombustionorpyrolysis, together with the quantity of air
that isentrainedor otherwise mixed into the mass. It is
commonly an unwantedby-productof fires (includingstoves,candles,oil lamps, andfireplaces), but may also be used forpest control(fumigation), communication (smoke signals), defensive and offensive
capabilities in the military (smoke-screen),cooking, orsmoking(tobacco,cannabis, etc.). Smoke is used in rituals
where incense, sage, or resin is burned to produce a smell for spiritual
purposes. Smoke is sometimes used as a flavoring agent, and preservative for
various foodstuffs. Smoke is also a component ofinternal
combustion engineexhaust gas, particularlydiesel exhaust.

Smoke inhalationis the primary cause of death in victims of
indoorfires.
The smoke kills by a combination of thermal damage,poisoningandpulmonaryirritation caused bycarbon monoxide,hydrogen cyanideand other combustion products.

Smoke is anaerosol(ormist) of solid particles and
liquid droplets that are close to the ideal range of sizes forMie scatteringofvisible light. This effect has been likened to
three-dimensional textured privacy glass[citation
needed]— a
smoke cloud does not obstruct an image, but thoroughly scrambles it.

Chemical
composition

The composition of smoke depends on the nature of the burning
fuel and the conditions of combustion.

Fires with high availability of oxygen burn at a high
temperature and with small amount of smoke produced; the particles are mostly
composed of ash, or with large temperature differences, of condensed aerosol of
water. High temperature also leads to production ofnitrogen oxides.Sulfur content yieldssulfur dioxide, or in case of incomplete
combustion,hydrogen sulfide.Carbon and hydrogen are almost
completely oxidized tocarbon dioxideand water.Fires burning with lack of oxygen
produce a significantly wider palette of compounds, many of them toxic.Partial oxidationof carbon producescarbon monoxide, nitrogen-containing materials
can yieldhydrogen cyanide,ammonia, and nitrogen oxides.Hydrogengas
can be produced instead of water.Content
ofhalogenssuch
aschlorine(e.g.
inpolyvinyl chlorideorbrominated flame
retardants) may lead to production of e.g.hydrogen chloride,phosgene,dioxin,
andchloromethane,bromomethaneand
otherhalocarbons.Hydrogen fluoridecan be formed fromfluorocarbons, whetherfluoropolymerssubjected to fire or halocarbonfire suppression
agents.Phosphorusandantimonyoxides
and their reaction products can be formed from somefire retardantadditives, increasing smoke toxicity
and corrosivity.Pyrolysisofpolychlorinated
biphenyls(PCB), e.g. from
burning oldertransformer oil, and to lower degree also of
other chlorine-containing materials, can produce2,3,7,8-tetrachlorodibenzodioxin,
a potentcarcinogen, and otherpolychlorinated
dibenzodioxins.Pyrolysis
offluoropolymers, e.g.teflon, in presence of oxygen yieldscarbonyl fluoride(which hydrolyzes readily to HF and CO2);
other compounds may be formed as well, e.g.carbon tetrafluoride,hexafluoropropylene,
and highly toxicperfluoroisobutene(PFIB).

Emission
of soot in the fumes of a largedieseltruck,
without particle filters.

Pyrolysisof burning material, especiallyincomplete combustionorsmolderingwithout
adequate oxygen supply, also results in production of a large amount ofhydrocarbons, bothaliphatic(methane,ethane,ethylene,acetylene) andaromatic(benzeneand
its derivates,polycyclic
aromatic hydrocarbons; e.g.benzo[a]pyrene, studied as acarcinogen, orretene),terpenes.Heterocyclic
compoundsmay be also
present.Heavier hydrocarbons may
condense astar;
smoke with significant tar content is yellow to brown.Presence of such smoke, soot, and/or
brown oily deposits during a fire indicates a possible hazardous situation, as
the atmosphere may be saturated with combustible pyrolysis products with
concentration above the upperflammability limit,
and sudden inrush of air can causeflashoverorbackdraft.

Presence of sulfur can lead to formation of e.g.hydrogen sulfide,carbonyl sulfide,sulfur dioxide,carbon disulfide, andthiols;
especially thiols tend to get adsorbed on surfaces and produce a lingering odor
even long after the fire. Partial oxidation of the released hydrocarbons yields
in a wide palette of other compounds:aldehydes(e.g.formaldehyde,acrolein, andfurfural), ketones, alcohols (often aromatic,
e.g.phenol,guaiacol,syringol,catechol, andcresols),carboxylic acids(formic acid,acetic acid, etc.).

The visibleparticulate
matterin such smokes
is most commonly composed ofcarbon(soot).
Other particulates may be composed of drops of condensedtar,
or solid particles of ash. The presence of metals in the fuel yields particles
of metaloxides.
Particles of inorganicsaltsmay also be formed, e.g.ammonium sulfate,ammonium nitrate, orsodium chloride. Inorganic salts present on
the surface of the soot particles may make themhydrophilic. Many organic compounds, typically
thearomatic hydrocarbons,
may be alsoadsorbedon
the surface of the solid particles. Metal oxides can be present when
metal-containing fuels are burned, e.g.solid rocketfuels
containingaluminium.Depleted uraniumprojectiles after impacting the target
ignite, producing particles ofuranium oxides.Magneticparticles,
spherules ofmagnetite-likeferrous ferric oxide,
are present in coal smoke; their increase in deposits after 1860 marks the
beginning of the Industrial Revolution.(Magnetic
iron oxide nanoparticles can be also produced in the smoke frommeteoritesburning
in the atmosphere.)Magneticremanence,recordedin
the iron oxide particles, indicates the strength of Earth's magnetic field when
they were cooled beyond theirCurie temperature; this can be used to
distinguish magnetic particles of terrestrial and meteoric origin.Fly ashis
composed mainly ofsilicaandcalcium oxide.Cenospheresare
present in smoke from liquid hydrocarbon fuels. Minute metal particles produced
byabrasioncan be present in engine smokes.Amorphous silicaparticles are present in smokes from
burningsilicones; small proportion ofsilicon nitrideparticles can be formed in fires with
insufficient oxygen. The silica particles have about 10 nm size, clumped
to 70-100 nm aggregates and further agglomerated to chains.Radioactive particles may be present
due to traces ofuranium,thorium, or otherradionuclidesin the fuel;hot particlescan be present in case of fires duringnuclear accidents(e.g.Chernobyl disaster)
ornuclear war.

Smoke particulates, like other aerosols, are categorized into
three modes based on particle size:

·accumulation mode,
ranging between 75–250 nm and formed by coagulation of nuclei mode
particles

·coarse mode, with particles in
micrometer range

Most of the smoke material is primarily in coarse particles.
Those undergo rapiddry precipitation, and the smoke damage in
more distant areas outside of the room where the fire occurs is therefore
primarily mediated by the smaller particles.

Aerosol of particles beyond visible size is an early indicator
of materials in a preignition stage of a fire.

Traces of vanadium in high-temperature combustion products form
droplets of moltenvanadates. These attack thepassivation layerson metals and causehigh temperature
corrosion, which is a concern especially forinternal
combustion engines. Moltensulfateandleadparticulates also have such effect.

Some components of smoke are characteristic of the combustion
source.Guaiacoland
its derivatives are products of pyrolysis ofligninand
are characteristic ofwoodsmoke; other markers aresyringoland
derivates, and othermethoxyphenols.Retene, a product of pyrolysis ofconifertrees,
is an indicator offorest fires.Levoglucosanis
a pyrolysis product ofcellulose.Hardwoodvssoftwoodsmokes
differ in the ratio of guaiacols/syringols. Markers for vehicle exhaust includepolycyclic
aromatic hydrocarbons,hopanes,steranes, and specific nitroarenes (e.g.1-nitropyrene). The ratio of hopanes and
steranes to elemental carbon can be used to distinguish between emissions of
gasoline and diesel engines.

Many compounds can be associated with particulates; whether by
beingadsorbedon
their surfaces, or by being dissolved in liquid droplets. Hydrogen chloride is
well absorbed in the soot particles.

Inert particulate matter can be disturbed and entrained into the
smoke. Of particular concern are particles ofasbestos.

Depositedhot particlesofradioactive falloutand bioaccumulated radioisotopes can
be reintroduced into the atmosphere bywildfiresandforest fires; this is a concern in e.g. theZone of alienationcontaining contaminants from theChernobyl disaster.

Polymers are a significant source of smoke. Aromaticside groups, e.g. inpolystyrene, enhance generation of smoke.
Aromatic groups integrated in the polymer backbone produce less smoke, likely
due to significantcharring. Aliphatic polymers tend to generate
the least smoke, and are non-self-extinguishing. However presence of additives
can significantly increase smoke formation.Phosphorus-based and halogen-basedflame retardantsdecrease production of smoke. Higher
degree ofcross-linkingbetween the polymer chains has such
effect too.

Visible and
invisible particles of combustion

Smoke
from awildfire

Smoke
rising up from the smoldering remains of a recently extingished mountain fire
in South Africa.

Thenaked eyedetects
particle sizes greater than 7 µm (micrometres).Visibleparticles
emitted from a fire are referred to as smoke.Invisibleparticles
are generally referred to as gas or fumes. This is best illustrated whentoastingbread in a toaster. As the bread heats
up, the products of combustion increase in size. The fumes initially produced
are invisible but become visible if the toast is burnt.

Anionization chambertypesmoke detectoris technically a product of combustion
detector, not a smoke detector.Ionization chambertypesmoke detectorsdetect particles of combustion that
are invisible to thenaked eye. This explains why they may
frequentlyfalse alarmfrom
the fumes emitted from the red-hot heating elements of a toaster, before the
presence of visible smoke, yet they may fail to activate in the early, low-heatsmolderingstage
of a fire.

Smoke from a typical house fire contains hundreds of different
chemicals and fumes. As a result, the damage caused by the smoke can often
exceed that caused by the actual heat of the fire. In addition to the physical
damage caused by the smoke of afire– which manifests itself in the form
of stains – is the often even harder to eliminate problem of a smoky odor. Just
as there are contractors that specialize in rebuilding/repairing homes that
have been damaged by fire and smoke,fabric restorationcompanies specialize in restoring
fabrics that have been damaged in a fire.

Dangers of smoke

Smoke from oxygen-deprived fires contains a significant
concentration of compounds that are flammable. A cloud of smoke, in contact
with atmospheric oxygen, therefore has the potential of being ignited – either
by another open flame in the area, or by its own temperature. This leads to
effects likebackdraftandflashover.Smoke inhalationis also a danger of smoke that can
cause serious injury and death.

Many compounds of smoke from fires are highly toxic and/or
irritating. The most dangerous iscarbon monoxideleading tocarbon monoxide
poisoning, sometimes with the additive effects ofhydrogen cyanideandphosgene. Smoke inhalation can therefore
quickly lead to incapacitation and loss of consciousness. Sulfur oxides,
hydrogen chloride and hydrogen fluoride in contact with moisture formsulfuric,hydrochloricandhydrofluoric acid, which are corrosive to both
lungs and materials. When asleep the nose does not sense smoke nor does the
brain, but the body will wake up if the lungs become enveloped in smoke and the
brain will be stimulated and the person will be awoken. This does not work if
the person is incapacitated or under the influence of drugs and/or alcohol.

Cigarette smokeis a major modifiable risk factor forlung disease,heart disease, and manycancers. Smoke can also be a component of
ambient air pollution due to the burning of coal in power plants, forest fires
or other sources, although the concentration of pollutants in ambient air is
typically much less than that in cigarette smoke. One day of exposure to PM2.5
at a concentration of 880 μg/m3, such as occurs in Beijing, China, is the
equivalent of smoking one or two cigarettes in terms of particulate inhalation
by weight.The analysis is complicated, however, by the fact that the organic
compounds present in various ambient particulates may have a higher
carcinogenicity than the compounds in cigarette smoke particulates.

Smoke can obscure visibility, impeding occupant exiting from
fire areas. In fact, the poor visibility due to the smoke that was in theWorcester
Cold Storage Warehouse fireinWorcester,
Massachusettswas the
exact reason why the trapped rescue firefighters couldn't evacuate the building
in time. Because of the striking similarity that each floor shared, the dense
smoke caused the firefighters to become disoriented.

The effect of smoke burning off the end of a tobacco product or
the smoke exhaled by a smoker is known as secondhand smoke. This smoke is
contained with harmful substances that can harm the body of the smoker. A
person could have serious health problems from the result of breathing in
secondhand smoke such as diseases or cancers. A child’s undeveloped body can
face respiratory problems that could affect their lives forever. Secondhand
smoke also harms the environment by being an indoor air pollutant that people
breathe in.

Smoke corrosion

Smoke contains a wide variety of chemicals, many of them aggressive
in nature. Examples arehydrochloric acidandhydrobromic acid, produced fromhalogen-containingplasticsandfire retardants,hydrofluoric acidreleased bypyrolysisoffluorocarbonfire suppression
agents,sulfuric acidfrom burning ofsulfur-containing materials,nitric acidfrom
high-temperature fires wherenitrous oxidegets formed,phosphoric acidandantimonycompounds
from P and Sb based fire retardants, and many others. Suchcorrosionis
not significant for structural materials, but delicate structures, especiallymicroelectronics, are strongly affected.
Corrosion ofcircuit boardtraces, penetration of aggressive
chemicals through the casings of parts, and other effects can cause an
immediate or gradual deterioration of parameters or even premature (and often
delayed, as the corrosion can progress over long time) failure of equipment
subjected to smoke. Many smoke components are alsoelectrically
conductive; deposition of a conductive layer on the circuits can
causecrosstalksand
other deteriorations of the operating parameters or even cause short circuits
and total failures.Electrical contactscan be affected by corrosion of
surfaces, and by deposition ofsootand other conductive particles or
nonconductive layers on or across the contacts. Deposited particles may
adversely affect the performance ofoptoelectronicsby absorbing or scattering the light
beams.

Corrosivity of smoke produced by materials is characterized by
thecorrosion index(CI), defined as material loss
rate (angstrom/minute) per amount of material gasified products (grams) per
volume of air (m3). It is measured by exposing strips of metal to flow of
combustion products in a test tunnel. Polymers containing halogen andhydrogen(polyvinyl chloride,polyolefinswith
halogenated additives, etc.) have the highest CI as the corrosive acids are
formed directly with water produced by the combustion, polymers containing
halogen only (e.g.polytetrafluoroethylene)
have lower CI as the formation of acid is limited to reactions with airborne
humidity, and halogen-free materials (polyolefins,wood)
have the lowest CI.[15]However, some halogen-free materials can
also release significant amount of corrosive products.

Smoke damage to electronic equipment can be significantly more
extensive than the fire itself.Cablefires are of special concern;low smoke zero
halogenmaterials are
preferable for cable insulation.

When smoke comes into contact with the surface of any substance
or structure, the chemicals contained in it are transferred to it. The
corrosive properties of the chemicals cause the substance or structure to
decompose at a rapid rate. Certain materials or structures absorb these
chemicals, which is why clothing, unsealed surfaces, potable water, piping,
wood, etc., are replaced in most cases of structural fires.

Secondhand tobacco smoke inhalation

Secondhand tobacco smoke is the combination of both sidestream
and mainstream smoke emissions. These emissions contain more than 50
carcinogenic chemicals. According to the Surgeon General's latest report on the
subject, "Short exposures to secondhand [tobacco] smoke can cause blood
platelets to become stickier, damage the lining of blood vessels, decrease
coronary flow velocity reserves, and reduce heart variability, potentially
increasing the risk of a heart attack".The
American Cancer Society lists "heart disease, lung infections, increased
asthma attacks, middle ear infections, and low birth weight" as
ramifications of smoker's emission.

Measurement

As early as the 15th centuryLeonardo da Vincicommented at length on the difficulty
of assessing smoke, and distinguished betweenblack smoke(carbonized
particles) and white 'smoke' which is not a smoke at all but merely a
suspension of harmless water particulates.Smoke
from heating appliances is commonly measured in one of the following ways:

In-line capture.A smoke
sample is simply sucked through a filter which is weighed before and after the
test and the mass of smoke found. This is the simplest and probably the most
accurate method, but can only be used where the smoke concentration is slight,
as the filter can quickly become blocked.

TheASTM smoke pumpis a simple and widely used method of
in-line capture where a measured volume of smoke is pulled through a filter
paper and the dark spot so formed is compared with a standard.

Filter/dilution tunnel.A smoke sample is drawn through a tube
where it is diluted with air, the resulting smoke/air mixture is then pulled
through a filter and weighed. This is the internationally recognized method of
measuring smoke fromcombustion.

Electrostatic precipitation.The smoke is passed through an array of
metal tubes which contain suspended wires. A (huge) electrical potential is
applied across the tubes and wires so that the smoke particles become charged
and are attracted to the sides of the tubes. This method can over-read by
capturing harmless condensates, or under-read due to the insulating effect of
the smoke. However, it is the necessary method for assessing volumes of smoke
too great to be forced through a filter, i.e., frombituminous coal.

Ringelmann scale.A measure of smoke color. Invented by
ProfessorMaximilian
Ringelmannin Paris in
1888, it is essentially a card with squares of black, white and shades of gray
which is held up and the comparative grayness of the smoke judged. Highly
dependent on light conditions and the skill of the observer it allocates a
grayness number from 0 (white) to 5 (black) which has only a passing
relationship to the actual quantity of smoke. Nonetheless, the simplicity of
the Ringelmann scale means that it has been adopted as a standard in many
countries.

Cossar
scale.The
change of atmospheric smoke particulate concentration resulting from the
presence of Barry Cossar. The ratio of smoke to air exiting Barry Cossar is
measured and compared against that in the surrounding atmosphere. This dynamic
scale ranges from zero to seven; reported measurements typically average very
near seven.

Optical scattering.A light
beam is passed through the smoke. A light detector is situated at an angle to
the light source, typically at 90°, so that it receives only light reflected
from passing particles. A measurement is made of the light received which will
be higher as the concentration of smoke particles becomes higher.

Optical obscuration.A light beam is passed through the smoke
and a detector opposite measures the light. The more smoke particles are
present between the two, the less light will be measured.

Combined optical methods.There are various proprietary optical smoke
measurement devices such as the 'nephelometer' or the 'aethalometer' which use several different
optical methods, including more than one wavelength of light, inside a single
instrument and apply an algorithm to give a good estimate of smoke. It has been
claimed that these devices can differentiate types of smoke and so their
probable source can be inferred, though this is disputed.

Inference fromcarbon monoxide.Smoke is incompletely burnedfuel,
carbon monoxide is incompletely burned carbon, therefore it has long been
assumed that measurement of CO influe gas(a
cheap, simple and very accurate procedure) will provide a good indication of
the levels of smoke. Indeed, several jurisdictions use CO measurement as the
basis of smoke control. However it is far from clear how accurate the
correspondence is.

Medicinal smoke

Throughout recorded history, humans have used the smoke ofmedicinal plantsto cure illness. A sculpture fromPersepolisshowsDarius the Great(522–486 BC), the king ofPersia, with twocensersin
front of him for burningPeganum harmalaand/orsandalwoodSantalum album, which was believed to protect
the king from evil and disease. More than 300 plant species in 5 continents are
used in smoke form for different diseases. As a method ofdrug administration,
smoking is important as it is a simple, inexpensive, but very effective method
of extracting particles containing active agents. More importantly, generating
smoke reduces the particle size to a microscopic scale thereby increasing the
absorption of its active chemical principles.